pH-Responsive Near-Infrared Emitting Gold Nanoclusters.

Area of Science:

• Nanotechnology
• Biophotonics
• Chemical Biology

Background:

• pH-responsive fluorophores are valuable tools for biological analysis.
• Gold nanoclusters offer unique optical properties for bioimaging.

Purpose of the Study:

• To develop a general method for creating pH-responsive near-infrared (NIR) emissive gold nanoclusters.
• To investigate the mechanism of pH-responsive emission in gold nanoclusters.
• To demonstrate the utility of these nanoclusters as probes for cellular imaging.

Main Methods:

• Synthesized gold nanoclusters functionalized with aliphatic tertiary amine (TA) ligands.
• Employed computational studies to elucidate the electronic structure changes related to pH response.
• Utilized fluorescence spectroscopy to characterize pH-dependent emission properties.
• Performed cellular imaging experiments to assess probe specificity and sensitivity for lysosomes.

Main Results:

• Successfully synthesized pH-responsive NIR-emitting gold nanoclusters.
• Demonstrated that protonation/deprotonation of TA groups modulates electronic structure and thus NIR emission.
• Observed decreased photoluminescence in basic conditions (pH 7-11) due to photo-induced electron transfer.
• Observed restored photoluminescence in acidic conditions (pH 4-7) as protonated TA groups inhibit electron transfer.
• Validated the use of these nanoclusters as specific and sensitive probes for lysosomes in live cells.
• Achieved non-invasive imaging with minimal interference from cellular autofluorescence.

Conclusions:

• Established an effective strategy for creating pH-responsive NIR gold nanocluster probes.
• The pH sensitivity is attributed to the electronic modulation of TA groups affecting electron transfer.
• These novel gold nanoclusters show significant potential for sensitive and specific lysosomal imaging in biological systems.